Method of delivering compositions to substrates

ABSTRACT

Method of delivering compositions to organic substrates, particularly lumber. Method involves heating a target zone of the substrate and then applying the composition to the surface of the substrate wherein the temperature of the composition is lower than that of the target zone of the substrate. Compositions include biocidal, strength modifiers, waterproofing and polymers.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/861,648, filed on Apr. 12, 2013, which is a continuation of U.S.patent application Ser. No. 10/539,685, filed on Aug. 9, 2006 (now U.S.Pat. No. 8,425,980) which is the national phase of InternationalApplication No. PCT/NZ2003/000277, filed on Dec. 12, 2003, which claimsthe priority benefit of New Zealand Patent Application No. 523249, filedon Dec. 16, 2002, the entire contents of each are incorporated herein byreference.

FIELD

This invention relates to methods of delivering compositions to organicsubstrates. In particular, the invention relates to methods ofdelivering compositions to lignocellulosic substrates, such as lumber.The methods may be for the purpose of prevention of growth of pestorganisms, or for providing specific properties to the substrate, forexample.

BACKGROUND

There are known methods for delivering a composition to a substrate.These techniques may vary depending on the nature of the substrate towhich a composition is to be applied, and whether or not the compositionis required to penetrate the surface of the substrate. Many of theseknown methods require complex machinery and also active pressure systemswhich require a lot of power input. There may be a number of otherdisadvantages of known methods. The following background discussionsoutline, by way |of example, techniques used to deliver compositions tolignocellulosic substrates such as freshly felled logs or processedlumber.

Lignocellulosic material, and more specifically debarked logs or sawnlumber, largely because these are of biological origin, are prone toattack by organisms such as bacteria, insects, nematodes and a varietyof fungi including decay and staining fungi. Such attack reduces theservice life of logs or lumber extracted therefrom, degrades theappearance of the logs or lumber, and reduces the service life of suchmaterials with resultant cost of replacement or potential hazard due tofailure.

Logs, or lumber, when freshly cut, generally are not contaminatedinternally by fungi. However, as soon as the wood substrate is exposedby either bark damage or by cutting, fungal spores attach to any exposedsurface and begin growing by utilising the available carbohydrates andresin acids as a food source. A number of fungal species includingOphiostoma species are known to grow rapidly into the substrate andquickly move beyond the control of readily available fungicides. Thereis also a window of opportunity for pest organisms to colonise suchsubstrates between the period of felling and the time at whichpesticidal treatments are applied. This infection by pest organismsprior pesticidal treatment may be referred to as “pre-infection” and isa significant problem for the lumber industry.

To mitigate infection by biological pests methods have been developed totreat these substrates with a variety of chemicals by various physicalprocesses. Unfortunately, these processes may be considered to have oneor more disadvantages. Some such processes and their disadvantages arenoted herein below.

Lignocellulosic substrates are complex structures including lumber cellsinterconnected by pits which include a membrane otherwise acting as avalve system when the tree is living. Such cells and cellinterconnections offer impedance to the flow of preservative into thesubstrate. This is more particularly so when the substrate is drybecause the pit membranes aspirate, that is they collapse to either sideof the pit and effectively seal it shut. Drying of the substrate howeveris important prior to treatment with preservative because space isrequired within which to place the preservative. Consequently a largenumber of variations of vacuum/pressure processes have been developed toovercome this impedance thus allowing flow of a composition (for examplea biocide or preservative composition) throughout the entire substrateto ensure total protection.

Several such processes include those of: 1) Rueping: Pre-pressure withgas followed by pressure with preservative or chemical solution; 2)Lowry: Pressure impregnation with preservative or chemical solution; and3) Bethel: Vacuum followed by pressure impregnation with preservative orchemical solution. These processes are described in “Industrial TimberPreservation”, 1979, J G Wilkinson, Associated Business Press.

The Rueping process applies pre-pressure with gas prior to treatmentwith preservative fluids. This pre-pressure with gas fills the cellswith a compressible medium such that after treatment with fluid the gaswill expand forcing out any surplus fluid. However this can result inongoing kickback of preservative contaminated fluid which may behazardous and which kickback fluid may contain extractives which willinterfere with preservative chemistry.

The Rueping and Lowry processes retain gas within the void spaces withinthe substrate. Thus, the impregnation process requires pumps to forcefluid into the substrate against the back pressure of the gases in thevoids.

The Bethel process removes all gases from the cells by application of avacuum which cells then become completely filled with preservativefluid. This method has the disadvantage that lumber is completely filledwith aqueous fluid which can not be sucked out again. Accordingly, thelumber takes considerable time to dry.

It is noted that some of these processes necessitate impregnation of upto 700 litres of chemical solution per cubic metre of lumber, in forexample softwoods.

These systems also have the disadvantage that preservative or chemicalcomposition is recycled back and forth between the pressure vessel andthe storage tanks. This can lead to contamination of the solution bylumber extractives. This can cause problems. For example, in cases wherepreservatives contain hexavalent chromium, lumber extractives in thepreservative composition may cause a chemical imbalance. Recycling ofcompositions can also be a problem where ammoniacal preservatives areused because ammonia can volatilise causing precipitation of othercomponents resulting in hazardous emissions. Use of alternativechemicals which are not necessarily preservatives also suffer from theseproblems.

There are examples of processes which attempt to alter the properties ofsome substrates such as lumber by impregnation with polymeric materials.Plant and equipment for such processes is very expensive. Large steelpressure vessels are required which must sustain positive pressures of600 pounds per square inch, or vacuum of nearly minus 15 pounds persquare inch. To assist these processes it is necessary to have large,high volume, high pressure pumps and, high volume, high vacuum pumps.Not only are these expensive, they must operate in quite corrosivechemical environments, which leads to costly repair and maintenance.Since the treatment plant is large and the pressure vessel may have acapacity of 30 cubic metres, it is necessary to have similar sizedstorage vessels to contain the operating fluid. Due to the size of theplant equipment and the risk of preservative spillage it is necessary tohouse the plant in a contained building. Accordingly, this type offacility is very capital expensive to build and operate.

A critical issue of all the above processes is the size of the operationand more significantly the need to store large volumes of hazardouschemicals.

Various other methods have been developed to treat lumber with variouscompositions. For example: U.S. Pat. No. 3,964,863 describes a methodwhich uses a pressure vessel for treatment of lumber in which thepressure of the impregnating fluid is increased isostatically in acontrolled manner causing the impregnating fluid to be distributedthroughout substantially all of the material; U.S. Pat. No. 4,303,705describes a method of treatment of lumber with water-bornepreservatives, such as CCA salts, in which the preservatives are forcedinto the lumber under pressure and the water-borne lumber treatmentmaterials are held within the lumber under pressure until they aredeposited as by precipitation or chemical affixation; and, U.S. Pat. No.4,433,031 describes a method of impregnating lumber with a preservativewherein the treatment is carried out by exposing the lumber, whilesubmerged in the treating solution, to one or more cycles of reducedpressure (i.e. vacuum) and elevated pressure.

Additional examples include: U.S. Pat. No. 4,466,998 which describes theuse of water-borne preservatives to impregnate lumber by the empty-cellpressure impregnation method without the precipitation of water-bornesalts such as chromium, copper and arsenic when lumber sugars enter thetreating solution during the kickback or pressure release phase of theempty-cell cycle. The lack of precipitation is obtained by maintainingthe preservative salts solution at a temperature between about 40degrees Fahrenheit and about 70 degrees Fahrenheit; and U.S. Pat. No.5,970,624 describes a lumber impregnation method which comprises aprocess to heat lumber, a process to place the heated lumbers under avacuumed pressure, a process to immerse the heated lumbers in processingagents under the vacuumed pressure, and a process to restore thepressure of the lumbers immersed in the processing agents under thevacuumed pressure to the air pressure, and to immerse the lumbers in theprocessing agents under the air pressure.

Further examples include: the method of U.S. Pat. No. 5,871,817 whichdetails immersing dry lumber in a preservative sustained by a smallhydrostatic head can achieve effective impregnation; the methoddescribed in U.S. Pat. No. 6,235,403 in which in one aspect lumber isimpregnated with a waterborne preservative such as CCA at elevatedtemperature and pressure; and the method of NZ 235036 which involvesimpregnating a lignocellulosic substrate to modify its physicalproperties (namely to increase density or harden the substrate) usingtraditional methods of vacuum pressure impregnation.

U.S. Pat. No. 5,871,817 describes a method which eliminates the need forlarge pressure and vacuum pumps. However, the plant is still complex andexpensive and the process requires storage of moderate volumes ofpreservative chemicals. This process relies on a limited hydrostatichead to impregnate the lumber by placing the dried lumber submersedunder preservative solution into a controlled depth dip tank. In suchcase the dried lumber at ambient temperature is submerged in apreservative solution.

As mentioned above, pre-infection of lumber with pest organisms, such asfungi, is a major problem for the lumber industry. A recent trend hasbeen to formulate mobile biocides that have the ability to penetrate ordiffuse into the substrate. Unfortunately these are often toxic and moresignificantly they may be readily washed from the substrate surface byrain if exposed to such immediately after application. Accordingly,other methods have been developed in attempts to effectively deliverbiocide compositions to the lignocellulosic material.

Whilst modern formulations have been developed which give a degree ofpenetration radially into the substrate surface, this movement is notlarge. Since the fungi of most concern are able to grow up to 1.5 mm perday under optimum conditions it is currently necessary to treat withchemical within approximately 48 hours of exposing fresh substratesurface. In most situations this is impractical and therefore analternative method of control or remediation is needed.

A particular difficulty in effectively treating lumber for or frompre-infection is that the lumber needs to be treated soon after felling.In this condition, the lumber contains a lot of moisture, as opposed toprocessed or milled lumber which will have been substantially dried. Themoisture content of this type of lumber may impede the absorption of abiocide composition into it to sufficient depth to prevent or remediategrowth of pest organisms, particularly fungi.

Attempts have been made to use vacuum and pressure impregnationprocesses (such as those described above) to force formulations into wetor saturated organic substrates to a depth which would control fungaland other pest attack. Unfortunately, ineffective penetration andexcessive processing costs may result.

As mentioned previously herein, there are a number of methods ofsterilisation of logs and lumber. Both hot water and steam at ambientpressure have been used to condition logs prior to conversion to veneer.Similarly steam at elevated pressure has been used commercially in polesand lumber to reduce moisture and to open pathways such as rayparenchyma such that pressure impregnation with preservatives can befacilitated. These methods however, may suffer from a number ofproblems.

Specific examples of methods which have been used in attempts to controlpre-infection of lumber are provided below. As with the examplesprovided above, such methods may suffer from one or more problems.

U.S. Pat. No. 5,505,240 describes the sterilisation of debarked logsusing hot water treatment. The process involves water in which thedebarked logs are immersed being heated indirectly using steam coilswhich are submerged in the water.

U.S. Pat. No. 5,447,686 describes sterilisation of logs using steam orhot water. The process may involve the addition to the steam of achemical comprising a biocide. This has some serious limitations in thatvolatile biocides must be used and which could pose severe risk tohealth. Additionally, in the case of hot water containing a biocidethere remains a large volume of biocide containing fluid and this posesan environmental risk particularly as it will also accumulateextractives from the logs and ultimately require disposal. More seriousdisadvantages of this process may be difficulty in having the biocideadequately penetrate the substrate and that prevention of cracking,checking and decay is not achieved.

McLean describes the principles, processes and times required to achievesterilisation and conditioning of substrates; MacLean, J. D. 1952.Preservative treatment of wood by pressure methods; US Department ofAgriculture, Agriculture Handbook No. 40. McLean however does notanticipate the consequence of moisture loss or the need to applysubsequent prophylactic treatments.

U.S. Pat. No. 4,978,501 describes a process for sterilisation ofmushroom casings using radio frequency energy. In this process casingswhich are typically comprised of lignocellulosic materials, are passedthrough an electromagnetic field. If sufficient power is applied forlong enough this will result in sterilisation of the substrate. Sincemushroom casings will be used immediately in relatively sterileenvironments there is no need to prevent re-infection.

U.S. Pat. No. 6,014,819 describes amelioration of fungal degrade byexposure of hardwood logs to steam. The process involves the moisturecontent of the substrate being maintained. Addition of biocides mayoccur during the heating process. This process may suffer from thenegative features associated with the process of U.S. Pat. No.5,447,686.

The above description and examples highlight the problems associatedwith known methods for treatment or impregnation of organic substrateswith compositions such as preservative compositions. Problems mayinclude one or more of: necessity to use expensive plant and processingequipment; large plant and processing equipment; extended processingand/or treatment times; excessive environmental impact; excessive energyrequirements; waste of treatment composition; ineffective delivery ofcomposition to target zones within the substrate being treated. Suchproblems may also exist in relation to treating organic substrates withother compositions.

OBJECT

It is an object of the present invention to provide an improved methodfor delivery of a composition to organic substrates, particularlylignocellulosic substrates, or at least to provide the public with auseful choice.

STATEMENT OF INVENTION

The inventor has unexpectedly discovered that effective delivery orimpregnation of a composition into a substrate, such as lumber, can beachieved by using the reduced pressure (or partial vacuum) created bythe rapid cooling of hot gases within the substrate when application ofa cool solution to the heated substrate occurs. This method does notrequire pressure pumps, vacuum pumps, large pressure vessel, largechemical storage facilities or a large treatment operation. Specificallyit allows use of simple and inexpensive plant with very low volumes ofstored chemical.

Accordingly, in a first broad aspect, the present invention provides amethod of delivering a composition to a substrate the method comprisingat least the steps of:

-   -   a) heating a target zone of a substrate; and    -   b) applying a composition to a surface of the substrate        comprising or immediately adjacent to the target zone; and        wherein the composition is at a temperature below that of the        target zone of the substrate.

Preferably, the substrate is an organic material. More preferably, thesubstrate is lignocellulosic. Preferably, the lignocellulosic substrateis lumber. In one aspect, the substrate may be in need of protection ortreatment to prevent or ameliorate growth of pest organisms.Alternatively, the substrate is an organic material to which certainother properties are desired to be imparted.

In one broad aspect of the invention, the lignocellulosic substrate issubstantially dry. In an alternative broad aspect of the invention, thelignocellulosic substrate contains a level of moisture; for example, thesubstrate may be green lumber. The substrate may be freshly felled anddebarked logs or freshly sawn lumber. Alternatively, the substrate isprocessed or milled lumber, more preferably it is high temperature kilndried lumber.

Preferably, a target zone of the substrate is heated and held at anelevated temperature for a period prior to application of thecomposition.

In the instance that the lignocellulosic substrate contains a level ofmoisture, the method of the invention may further comprise the step ofcontrolling loss of moisture from the target zone of the substrateduring step a) or during any period within which the target zone of thesubstrate is held at an elevated temperature.

Preferably, the period of time the target zone of the substrate is heldat an elevated temperature is a time sufficient to substantially heat toa uniform temperature, the entire target zone of the substrate. Morepreferably, the period is a time sufficient to sterilise at least atarget zone of the substrate.

In one embodiment, the target zone of the substrate is heated to atemperature such that the temperature differential between the targetzone and the composition at the time of application is 80 degreesCelsius.

Preferably, the target zone of the substrate is heated using a heatingfluid. Preferably the fluid is a gas or liquid. Where liquid, the fluidis preferably hot water. Where gas, the fluid is preferably hot air orsteam. Where steam, the fluid is preferably saturated steam or highpressure steam.

Alternatively, the target zone of the substrate is heated using radiofrequency energy or microwave energy.

In one aspect, the pressure conditions are controlled during step a.

Preferably, the composition is a biocidal composition. Alternatively,the composition is one which may impart properties of higher density orstrength to at least a target zone of the substrate. Preferably, thecomposition is of a polymeric or pre-polymeric nature. Preferably, thecomposition is an aqueous solution.

Preferably the composition is applied to the substrate by dipping,deluging, spraying, or brushing. Additionally, variations of vacuum orpositive pressure impregnation may be used.

Preferably, the composition is applied as an in-line process. Morepreferably, the composition is applied to the substrate as part of anin-line drying process using microwave energy.

Preferably, the method is an in-line process where the substrate isheated and the substrate is sprayed or deluged in the composition.

Alternatively, the method is a batch method wherein two or moresubstrates are treated simultaneously.

Preferably, the composition is applied at ambient temperature.

Preferably, the composition is stable at the temperature of thesubstrate at the time of application.

In the case of a lignocellulosic substrate required to be treated toprevent or ameliorate growth of pest organisms, such as duringpre-infection, the target zone preferably comprises an area from thesurface of the substrate to a depth of between approximately 0.1centimetres to approximately 4 centimetres.

In accordance with the above, in a further particularly preferred formof the invention there is provided a method of delivering a biocidalcomposition to a lignocellulosic substrate, the method comprising atleast the steps of:

-   -   a) heating a target zone of the lignocellulosic substrate; and    -   b) applying a biocidal composition to a surface of the substrate        comprising or immediately adjacent to the target zone;        wherein the biocidal composition is at a temperature below that        of the target zone of the substrate.

In another broad aspect, the invention provides a substrate to which acomposition has been delivered in accordance with a method of theinvention.

The invention may also be said broadly to consist in the parts, elementsand features referred to or indicated in the specification of theapplication, individually or collectively, in any or all combinations oftwo or more of said parts, elements or features, and where specificintegers are mentioned herein which have known equivalents in the art towhich the invention relates, such known equivalents are deemed to beincorporated herein as if individually set forth.

FIGURES

These and other aspects of the present invention, which should beconsidered in all its novel aspects, will become apparent from thefollowing description, which is given by way of example only, withreference to the accompanying figures, in which:

FIG. 1: Illustrates the rate of temperature change in fully watersaturated log billets when exposed to live steam at 100 degrees Celsiusand compares the temperature change at different depths from the logsurface; and

FIG. 2: Refers to FIG. 1 and illustrates the accumulated averagemoisture loss from the log billets with respect to time.

DETAILED DESCRIPTION OF INVENTION

The following is a description of the preferred forms of the presentinvention given in general terms in relation to the application of thenovel method. While the description focuses particularly on the deliveryof compositions to lumber or logs, and more particularly focuses ondelivery of biocidal compositions to remedy infection of lumber by pestorganisms, it should be appreciated that the method may be equallyapplicable to the delivery of alternative compositions and the treatmentof alternative substrates.

In general terms, the invention relates to methods of delivering acomposition to a substrate, preferably an organic substrate. The methodallows for absorption by, or impregnation of, the substrate by acomposition without the necessity of having to apply active pressuresystems.

The method of the invention may be used to deliver any fluid compositionto a substrate. The composition is preferably an aqueous solution andhas active components which are non-volatile at the temperature of thesubstrate at the time of application. Compositions of the invention maycontain polar and/or non-polar solvents and the like, for examplealcohol, and vegetable oils. Persons of general skill in the art towhich the invention relates will no doubt appreciate variouscompositions that may be applicable to the invention. However, by way ofexample, where treatment or prevention of infection or pre-infection bypest organisms is desired, compositions (biocide or biocidalcompositions) having pesticidal (fungicidal, bactericidal, insecticidalfor example) or preservative properties may be used. Where it is desiredthat the substrate has increased density or strength properties,compositions containing certain polymeric or pre-polymeric componentsmay be useful. Similarly, compositions may include those of use inwaterproofing a substrate. Additionally, compositions containing certaindyes to colour the substrate may be used.

Whilst not wishing to be bound by any particular theory, the inventorbelieves that the invention works through the creation of gas filledvoids in the substrate at elevated temperature into which the biocidecomposition (at lower temperature) is drawn following application.

As used herein, “substrate” should be taken to mean any organic materialwhich may be in need of delivery of a composition of some nature; forexample for the purposes of protection or treatment to prevent orameliorate growth of pest organisms. Such substrate is preferablylignocellulosic, for example living trees, wood products, lumber orlogs. The invention may be applicable to substrates containing a levelof moisture, or those which are substantially dry.

In the case of lignocellulosic substrates, those which “contain a levelof moisture” include freshly felled and debarked logs or freshly sawnlumber (so called green lumber). Those of general skill in the art towhich the invention relates will be aware that freshly felled logs orfreshly sawn lumber will contain approximately 150 percent of their dryweight as moisture if softwoods and approximately 80 percent ifhardwoods.

Again, at least in the case of lignocellulosic substrates, those whichare “substantially dry” include lumber dried by traditional methods.Such lumber may contain moisture of approximately 5 to approximately 30percent as a weight proportion of the lumber dry weight. Substantiallydry lignocellulosic substrates include lumber which has been processedvia kiln drying and the like and may have been milled to a final, ornear final product, for example a lumber composite material.

“Pests” or “pest organisms”, as referred to herein, may include anyorganisms which may infect an organic substrate, such as wood. While theinvention is particularly applicable to fungi, pest organisms may alsoinclude bacteria, insects, nematodes and the like.

When used herein, the terms “treatment” or “remediation” should be takenin their broadest possible contexts. They should not be taken to implythat a substrate is treated such that pest organisms are totallyremoved, although this is preferable. Prevention and amelioration ofgrowth of pest organisms is also encompassed by the invention.

In one preferred embodiment, the method comprises at least the steps of:

-   -   a) heating a target zone of a substrate; and    -   b) applying a composition to a surface of the substrate        comprising, or immediately adjacent, to the target zone;        wherein the composition is at a temperature below that of the        target zone of the substrate.

As used herein, a “target zone” of the substrate is any zone to which itis desired to have a composition delivered. A target zone may comprisethe entire substrate or any one or more parts thereof. In the case ofthe compositions being delivered for the purpose of treatment ofinfection by a pest organism, the target zone may be an area of a logwhich is susceptible to infection, or has been infected, by a pestorganism; for example, the target zone may comprise an area from thesurface of the substrate to a depth of between approximately 0.1centimetres to approximately 4 centimetres. Persons of general skill inthe art to which the invention relates will readily appreciate targetzones. Target zones may become further apparent from the examplesprovided hereinafter.

In a particularly preferred embodiment of the invention, a target zoneof the substrate is heated and held at an elevated temperature for aperiod prior to application of the composition.

As used herein, the “period of time” a target zone of the substrate isheld at an elevated temperature is a time sufficient to substantiallyheat to a desired temperature, the target zone of the substrate. In aparticularly preferred embodiment, the period is a time sufficient tosterilise at least a target zone of the substrate.

An “elevated temperature” is one which is higher than the temperature ofthe composition to be used in the method. More particularly, an elevatedtemperature is one sufficient to allow moisture loss from the substrate,or expansion of gases, within the substrate. In another embodiment, thetemperature is sufficient to assist in sterilisation of at least atarget zone of the substrate.

It should be appreciated that temperatures and times sufficient to heatand/or sterilise a target zone of a substrate may vary depending onfactors such as the nature of the substrate, the means used to heat thesubstrate, the composition to subsequently be applied, the desireduptake and penetration of composition required and in the instance oftreating a substrate against pest attack, the nature of the pests whichmay be present on the substrate. However, by way of example, in the caseof lumber, to be sterilised using steam against growth of fungi, theinventor contemplates sterilisation times of from 20 to 150 minutes andtemperatures ranging from approximately 50 to 250 degrees Celsiusdepending on equipment available and the depth from the surface to whichsterilisation is required. Further exemplary temperatures and times areprovided herein after under the heading “Examples”.

It should be appreciated that use of the phrase “sufficient tosterilise” does not imply that the sterilisation process must besufficient to completely rid the substrate of viable pest organisms. Theinventor contemplates a reduction in any viable pest organisms beingappropriate in respect of the invention. Additionally, there may beinstances where a substrate does not actually contain viable pestorganisms prior to sterilisation.

It will be appreciated that the temperature differential between targetzone of the substrate and the composition at the time of its applicationmay vary depending on the substrate to be treated and the nature of thecomposition to be applied. It will also be appreciated by persons ofgeneral skill in the art that the temperature differential may beadapted to control the level of penetration of composition intosubstrate. By way of general example, in certain cases the greater thetemperature differential (to a limit), the greater the possible pressurechange (as described herein after), with the possibility of greaterpenetration of composition into at least the target zone of thesubstrate. It should be appreciated that the temperature differentialmay be varied by varying the temperature to which a target zone of thesubstrate is heated, or by varying the temperature of the composition tobe applied to the substrate. However, in one embodiment of theinvention, the target zone of the substrate is heated to a temperaturesuch that the temperature differential between the target zone and thecomposition at the time of application is approximately 80 degreesCelsius. However, the inventor contemplates higher differentialsproviding reduced processing time and energy savings, especially wherethe entire substrate is not required to be heated. Accordingly, in otherembodiments, the temperature differential is greater than 80 degreesCelsius, more preferably approximately 100 degrees Celsius or greater.

The target zone of the substrate may be heated by any means suitable fordoing so. In a preferred embodiment, this is done using a heating fluid,for example any gas or liquid. Where liquid, the fluid is preferably hotwater. Where gas, the fluid is preferably hot air or steam. Where steam,the fluid is preferably saturated steam or high pressure steam. In oneembodiment of the invention, the fluid may contain a biocide. While theheating step may be conducted at atmospheric pressure, the inventionencompasses heating at elevated pressure. Similarly, the heating stepmay occur under conditions which control or constrain pressure.

Alternatively, the target zone of the substrate is heated using radiofrequency energy or microwave energy. In the case of radio frequencyheating wavelengths of greater than 2.4 GHz are preferable. Morespecifically, wavelengths of approximately 27 to 40 MHz are particularlydesirable. At this range of wavelength, batches of two or more separatepieces of a substrate, for example two or more logs of lumber may betreated simultaneously.

The composition may be applied to a surface of the substrate using anyknown means of bringing a composition into contact with a material. Byway of example, the composition is applied by dipping, deluging,spraying, or brushing. While the inventor does not believe it necessaryto apply active pressure to effect delivery of a composition inaccordance with the invention, there may be instances where the activepressure systems (positive pressure or vacuum) may be desirable.

As mentioned herein before, the composition is applied to the substrateat a temperature below that of the target zone at the time ofapplication. Preferably, certain temperature differentials apply, asmentioned above. While the operating temperature of the composition mayvary depending on the nature of the biocide, for example its solubilityand the like, the composition is preferably at ambient temperature orlower.

As mentioned hereinbefore, the method of the present invention isapplicable to substrates which are substantially dry, and those whichcontain a level of moisture. Where the substrate contains a level ofmoisture, for example green lumber, the method of the invention mayfurther comprise the step of controlling loss of moisture from thetarget zone of the substrate during step a) or during any period withinwhich the target zone of the substrate is held at an elevatedtemperature.

Moisture loss may be controlled by manipulation of temperature, thehumidity of the surrounding medium, and or the atmospheric pressureconditions. For example, a fluid medium of high humidity or a fluidmedium of high pressure may be used to reduce moisture loss. Preferablythe fluid is a gas or liquid. Preferably, where the fluid is a liquid,it is hot water. In the case of a gas, the gas is preferably hot air, ormore preferably steam. In a particularly preferred form of theinvention, the fluid medium is saturated steam or high pressure steam.In a further preferred example, the pressure conditions are constrainedto prevent moisture present in the substrate from boiling. For example,the substrate may be heated using radio frequency, while simultaneouslycontrolling pressure conditions. At a desired time and temperature thepressure constraints may be removed allowing any moisture to boil andthus be expelled from the substrate. At a time subsequent to themoisture loss, but whilst the substrate is still at elevatedtemperature, a composition of lower temperature is applied (for exampleby immersing the substrate in the composition). Such techniques arefurther exemplified hereinafter under the heading “Examples”.

The method of the invention may be adapted to in-line processing. Forexample, in one embodiment, the inventor contemplates logs being heatedfor a controlled time in a chamber containing live steam atapproximately 100 Celsius using appropriate mechanisms such as chainfeeds with the logs moving progressively through the chamber. Subsequentto heating the logs may then move into a second chamber where moistureloss is controlled without substantial temperature drop. Either in thatchamber or immediately subsequent the logs are dipped or deluged withpreservative solution. A similar in-line process can be applied forexample to microwave heated lumber wherein the lumber passes through awaveguide where it is exposed to microwave energy sufficient to raisethe temperature of the substrate. Immediately upon discharge from thewaveguide the lumber enters a dip tank or deluge booth where it isuniformly exposed to preservative chemical.

The processes of the invention might conveniently be combined withstandard lumber planing operations. For example, after planing thelumber passes into an accumulator in which the lumber is heated. After acontrolled time the lumber passes out immediately followed by a delugespray or dip in a desirable composition. This could be described as anin-line system or continuous process and since each piece of lumber issmall the required volume of preservative or chemical solution is alsosmall. Such a system may require only 0.2 to 0.5 cubic metres ofoperating solution compared to a volume of 30 cubic metres for a typicaloperation in common use.

As an alternative to in-line processing, the invention may be applied tobatch processing, which may provide an efficient and cost effectiveprocedure. This is particularly the case where steam or radio frequency(RF) heating is employed. As mentioned herein before, where wavelengthsof between, for example 27 to 40 MHz are used, a number of logs may besufficiently heated simultaneously. Skilled persons may readilyappreciate appropriate wavelengths outside this range.

As will be appreciated, as the composition is applied to the heatedsubstrate in accordance with the method of the invention, it cools thesubstrate causing any gases held within the substrate (as a result ofheating and moisture loss) to contract and/or condense. This creates apressure drop and draws the composition into at least the target zonewhich has been heated and/or sterilised. It would be an advantage if thecomposition itself had properties which allowed it to penetrate thesubstrate to some extent (as opposed to just sitting on its surfacefollowing application); in this way, the composition may penetratebeyond the target zone. Skilled persons will readily appreciatecompositions having desirable penetrative properties.

A novel feature of the invention includes the ability to use otherwiseheat sensitive compositions, for example preservative solutions such asthose aforementioned, like copper chrome arsenate. This is because moreor less only the solution which enters the substrate will endure heatingand then only for a very short time. There will be no kickback andtherefore there will be no contamination or decomposition of thecomposition being used. Effectively each piece of lumber can be treatedwith virgin composition and which composition can be controlledprecisely unlike previously used processes. It is envisaged that nocontaminated sludge will be generated. Thus this invention may offeradditional advantages over traditional processes.

EXAMPLES

The invention will now be further described with reference to thefollowing non-limiting examples.

Example 1

Many organic substrates are susceptible to attack by pest organisms.There are recognised problems with gaining effective penetration ofsubstrates by biocide compositions to effectively prevent or treatinfection by such pests. Similarly, problems are associated with delaysbetween collection of organic substrate material and processing to finalproducts, including preservation steps; during this time, there is awindow of opportunity for pests to attack the substrate. This may bereferred to as “pre-infection” and is of particular significance in thelumber industry as is described elsewhere herein. Pre-infection by fungiis a significant problem.

The impact of fungal degrade on wood has been described by variousauthors. “Antisapstain Treatment of Logs and Lumber in New Zealand.Wakeling et al, 2001. Proceedings ExpoCORMA International Conference,Chile”, teaches of the severity of the problem of pre-infection. In anattempt to remedy the pre-infection, people have studied newformulations designed to penetrate further into the substrate, “Sentry,a new antisapstain formulation for protecting logs and lumber, parts 1 &2, Wakeling et al, IRG Conference 2002, Germany”.

The problem is described as rapid radial growth of fungi into thesubstrate during the early stage from felling to processing. Whilst somestaining fungi consume available carbohydrates in the form of sugars,others move rapidly through the ray parenchyma consuming triglyceridessuch as wood resins. Because some fungal species particularly someOphiostoma are able to grow at around 1.5 millimeters per day,prevention of degrade dictates immediate processing and treatment.Whilst the more recently developed biocide compositions do penetratesomewhat into the substrate, subsequent research by the above authorsand others has confirmed that with current formulating technology thewindow of opportunity of control can be extended to no more than 48hours.

Due to the frequently difficult terrain and other extractionconstraints, most logs felled can not be processed within this timewindow. Therefore the problem of pre-infection remains and still causeslosses of many millions of dollars.

Attempts have been made to apply temporary prophylactic treatments atthe time of felling. This is incompletely successful because the logwill be damaged further after treatment allowing ingress ofre-infection. Further this process is restricted to relatively flat landwhere mechanical harvesters are used and this comprises a smallproportion of total trees felled.

Other attempts have been made to control pre-infection using varioussterilisation processes. Historical methods often used steam and hotwater and normally relied on long treatment times to ensure heating ofthe substrate throughout. In more recent times consideration has beengiven to use of microwave radiation because this can rapidly heat thesubstrate throughout.

In some circumstances heat sterilisation alone will sufficientlyremediate degradation to allow lumber processing to be completed.However the sterile condition generated is temporary in that immediatelyupon exposure of sterilised wood to the environment it again encountersfungal spores which will re-infect the substrate. With sufficient delayin reapplying a preservative this re-infection will degrade thesubstrate, such as would occur with the prolonged storage andtransportation times associated with shipping logs or green lumber toforeign markets.

Application of a prophylactic treatment subsequent to sterilisation willcontrol this reinfection to some extent, but has limitations becausesuch treatments remain on the surface of the substrate, with subsequentloss of efficacy.

In some circumstances it may not be necessary to sterilise the entiresubstrate. Trees are relatively self protecting when alive, afterfelling, cutting or bark damage however, organisms may infect thesubstrate from the outside in. The zone of sterilisation may be thatwhich only includes the area which the pest, such as fungi, haspenetrated since the time of felling. This may be a few millimetres toseveral centimetres depending on the time from felling to treatment.This is an important consideration because not only is the cost ofenergy critical but also shorter heating times allows higher plantthroughput reducing the impact of cost of capital.

Traditional heat sterilisation causes considerable loss of moisture fromthe substrate with serious consequences. Drying of the substrate, whichis concomitant to moisture loss, makes milling more difficult due toincreased toughness of the substrate and wear on cutting edges such assaw blades. More significantly, during veneer production from logs, suchpeeling of drier material is more difficult, the knives used incurincreased wear, and even more significantly the veneer will splitresulting in a downgrade in value.

Furthermore, moisture loss may result in checking and splitting from thesurface of the substrate. Such checks and splits constitute direct openpathways for ingress of biological infection at depth within thesubstrate. The consequences could be complete failure of the substrate.

Application of a typical fungicidal formulation by typical processes maybe of limited value because the substrate is handled in a fashion priorto final use that will damage the surface and which will expose sterilebut unprotected substrate to fungal attack. Because green logs are ofconsiderable dimension and weight, very heavy duty handling equipment isrequired. Frequently the tines of fork lifts and loaders will bruiseand/or penetrate the substrate surface to some depth, possibly as muchas 2 or 3 centimetres. Any superficial treatment will be penetrated andingress of infection will occur. This breaching of treatment also occurswith checking and splitting from subsequent drying.

Surprisingly, the inventor has found that if a substrate susceptible toattack by pests is brought to an elevated temperature while controllingmoisture loss from the substrate, and substantially immediately treatedwith a biocide composition at a lower temperature, significantenhancement in biocide penetration into the substrate will occur.

In experiments leading to the invention, the inventor carried outstudies on several heating fluids to establish the heating time and heatprofile for Pinus radiata and other species. Recognising that the depthof sterilisation can be adjusted to meet the requirements of theextraction to processing window, that is the depth to which the fungiwill have penetrated at 1.5 millimeters per day (see Table 1),measurements were made at 3 depths.

TABLE 1 Depth (mm) Time window (days) at 1.5 mm/day 10 6.6 25 15.7 4323.7

It is generally accepted that 7 to 10 days from felling to processing isachievable and therefore sterilisation of an annulus of approximately 10mm is acceptable.

In anticipation of the need to sterilise an annulus around thesubstrate, temperatures were measured at various distances radially intothe substrate from the surface. Times are illustrated in FIGS. 1 and 2.

Because the heating medium is able to operate at 100 percent humidity,moisture loss during the heating step is expected to be negligible,although there may be some loss from thermal expansion of water andresidual air within the substrate.

Although a gradual moisture loss was anticipated from the substratesubsequent to heating, the inventor found, surprisingly, that theimmediate moisture loss is significant with a subsequently rapidlydiminishing rate of further moisture loss (FIG. 2). The moisture lossshown in FIG. 2 is the average moisture loss in the entire substrate.

Since the loss is occurring only in the sterilised zone it can berecognised that the actual loss in that zone is the average moistureloss at a point in time multiplied by the ratio of the total area of thecross section of the log divided by the cross section area of the zone,which is the annulus treated. It can be seen that within approximately15 to 30 minutes moisture loss can be greater than 6 percent in thesterilised zone and that is adequate void space to either create apressure drop by sudden cooling with biocide formulation, or foreffective pressure impregnation with biocide formulation.

The inventor believes that because the zone of sterilisation is smallthat the moisture loss is more or less restricted to the target zone.Understanding that

pV = nRT  for  a  fixed  mass  of  gas  or$\frac{P_{1}V_{1}}{T_{1}} = \frac{P_{2}V_{2}}{T_{2}}$

Subsequent application of a cooler fluid reduces the pressure of the gaswithin the empty cells to an extent that the fluid may be drawn into thesubstrate. If a temperature differential of 80 Celsius is achieved thismay result in a pressure differential of around 5 pounds per squareinch. Since this is negative pressure it is more than adequate to drawthe biocide composition into the substrate. The inventor contemplatesthat such movement is likely to be some distance, essentially throughall void space.

Having previously developed penetrating biocide systems the inventorconcluded that use of such low pressure assisted penetration of thebiocide might gain further benefit due the subsequent movement of thebiocide yet further into the substrate.

Broadly interpreting the results the inventor concluded thatsterilisation of a zone (annulus) suitable for a felling to processingtime of 7 days would require sterilisation to a depth of approximately10 millimetres, in the case of prevention or treatment of fungal growth.In this example, since the entire zone must remain at least 56 degreesCelsius for 30 minutes the total time for sterilisation is approximately50 minutes. Times for greater or lesser depths can be calculatedaccording to the charts herein.

Since small moisture loss can create sufficient negative pressure withwhich to draw in biocide formulation the Figures provided hereinillustrate that the period following sterilisation but prior toapplication of biocide can be selected from 0.1 minutes up to an hour ormore. However since the additional moisture loss offers no great benefitand, in fact, could be a disadvantage, the time is preferably between0.5 and 30 minutes.

The problem of biological infection occurring and developing in logs andlumber to an extent such that it cannot be readily remedied by knownmethods is of considerable concern to the industry. Attempts have beenmade to prevent the development of this infection by applying biocidesto the tree during the felling process. Unfortunately due to thedifficulty in gaining complete application this has limited efficacy.Further it does not overcome damage which occurs subsequent totreatment.

The present examples illustrate methods of mitigation of pre-infectionin lignocellulosic substrates which comprise sterilisation of thesubstrate in a heating fluid during which, or subsequent to, controlledmoisture loss is allowed. This creates sufficient gas filled voids inthe substrate into which a biocide composition can be applied by vacuumor pressure methods.

In recognition of two critical issues relating to mitigation ofpre-infection the inventor notes that the depth of sterilisation willdepend on the species concerned, the time from felling to processing andthe time from processing to final use. When the time from felling totreatment is relatively short it is most economical to treat arelatively shallow annulus around the substrate. This is beneficialbecause it reduces energy costs. The second issue of excess moistureloss is controlled by the type of heating medium, the duration ofheating and the timing of the application of the fungicidal formulationand therefore in the substrate the final moisture loss may be reduced.

Further because the biocide formulation may be drawn into the substrateby controlling moisture content and temperature of the substrate thishas a significant benefit because it is able to control any spores orgrowing fungi which may be at the limit of the sterilisation zone.

In fact there are additional commercially important benefits from this.If the ‘biocide is applied in a fashion which encourages penetration tosome depth below the surface this will protect the substrate from attackby fungi through checks, splits or regions of physical damage caused byhandling. This benefit is more so when fungicides with penetratingproperties are used in conjunction with this invention.

On the basis of this experimentation, the inventor learned thatimmediately subsequent to sterilisation gas containing voids in thesubstrate could be cooled creating a negative pressure which could beencouraged to take up biocide compositions in a fashion which offered anumber of benefits, namely:

-   -   The biocide replaced much of the lost moisture reversing the        effects of moisture loss (for example checking and splitting)        which would have otherwise occurred    -   The biocide, in replacing moisture loss, reduced the downstream        effects on plant and equipment and the damage which would        otherwise occur to the likes of veneers produced from the        substrate    -   By being drawn substantially into the substrate the biocide is        able to prevent reinfection both on the surface and more        particularly in areas where checking, splitting or mechanical        damage would otherwise expose sterile but unprotected substrate

Further, the inventor is aware that current biocide technology can notprovide sufficient efficacy for logs which are more than 48 hours fromfelling. However, if the pre-infected annulus is completely sterilisedby the process of this invention the effective time from felling may bereturned to zero, that is the sterile condition as existed in theoriginal tree.

The inventor has concluded that a process or method described herein mayoffer a practical and inexpensive alternative which can remedypre-infection in logs and green lumber and which may significantlyreduce the value otherwise lost to the downgrade of these materials dueto disfigurement or decay.

The enhanced penetration observed by the inventor is believed to haveboth commercial and environmental consequences. If the preservativeformulation has enhanced control of wood degrading organisms this mightallow a reduced loading of chemical in the treated substrate withoutloss of performance. This may be achieved by using less concentratedbiocide solutions which has an environmental benefit. The lower rate ofapplication also allows a reduction in the cost of treatment.

Example 2

Using the principles applied in relation to the above examples, theinventor set out to study whether the invention was applicable to lumberwhich was substantially dry. The inventor obtained samples of Montereypine (Pinus radiate) and Baltic pine (Pinus sylvestrus) which is verysimilar to Ponderosa pine (Pinus ponderosa). Some of these samples werehigh temperature kiln dried by traditional methods and some were driedusing conventional air drying known to those versed in the art of lumberdrying.

The samples were flat sawn, that is the growth rings were parallel tothe wide face of the samples. The sample dimensions were 100 mm by 50 mmby 150 mm in length. 100 mm by 50 mm is the typical cross section lumberused in house frame and for other purposes.

Duplicate studies used samples which were finished by planing thesurface; others were left in rough sawn state.

In all cases control samples were also included in the study but whereinthe heating step 20 was omitted.

Example 2A

High temperature kiln dried lumber samples were heated to 100 Celsiusfor 30 minutes in hot air. Subsequent to heating the samples wereimmediately quenched in an aqueous acidic copper containing preservativesolution and were left in the solution for 2 minutes. Such solution wasat ambient temperature.

A copper containing preservative was selected because solutions of thismetal are commonly used as lumber preservatives and also because it is asimple process to determine distribution of the preservative within thesubstrate by use of a simple colour change spot test. In these studiespyridyl azo naphthol was used as the spot test reagent because it is asensitive detector of copper.

Subsequent to treatment the samples were allowed to dry. They were thensectioned parallel to the face and spot tested with pyridyl azo naphtholdissolved in ethanol. The entire exposed face turned dark crimson redindicative of the presence of copper and which indicates completedistribution of the preservative.

The results of this study using the above detection method showed thatcomplete penetration and distribution throughout the lumber samplescould be achieved.

Example 2B

High temperature kiln lumber samples were heated to 150 Celsius for 30minutes in hot air. Subsequent to heating the samples were immediatelyquenched in an aqueous acidic copper containing preservative solutionand were left in the solution for 2 minutes. Such solution was atambient temperature.

Subsequent to treatment the samples were allowed to dry. They were thensectioned parallel to the face and spot tested with pyridyl azo naphtholdissolved in ethanol.

The results of this study using the above detection method showed thatcomplete penetration and distribution throughout the lumber samplescould be achieved.

Example 2C

Air dried lumber samples were heated to 150 Celsius for 30 minutes inhot air. Subsequent to heating the samples were immediately quenched inan aqueous acidic copper containing preservative solution and were leftin the solution for 1 minute. Such solution was at ambient temperature.

Subsequent to treatment the samples were allowed to dry. They were thensectioned parallel to the face and spot tested with pyridyl azo naphtholdissolved in ethanol.

The results of this study using the above detection method showed thatcomplete penetration and distribution throughout the lumber samplescould be achieved.

Example 2D

Air dried lumber samples were heated in a conventional kitchen microwaveoven operating at 900 watts for 60 seconds. Subsequent to heating thesamples were immediately quenched in an aqueous acidic copper containingpreservative solution and were left in the solution for 1 minute. Suchsolution was at ambient temperature.

Subsequent to treatment the samples were allowed to dry. They were thensectioned parallel to the face and spot tested with pyridyl azo naphtholdissolved in ethanol.

Results were as for example 2A.

The same preservative solution was used for all the above examples suchthat any changes in appearance or composition could be noted. During theprocess and subsequently 5 days later the composition remained clear andof consistent composition.

As noted previously herein, some known methods of biocide treatmentnecessitate uptake of fluids into dried lumber as high as 700 litres percubic metre. In the above studies uptakes ranged from 50 litres to 100litres depending on the temperature generated within the substrate andthe length of exposure of the heated substrate to the application fluid.

Conveniently the composition or strength of the compositions used can beadjusted in strength to achieve the various requirements of the finaluse of such substrates.

The results of this study using the above detection method showed thatcomplete penetration and distribution throughout the lumber samplescould be achieved.

Thus the inventor learned that immediately subsequent to heating, gasfilled voids in the substrate could be encouraged to take uppreservative or other chemical compositions by the cooling actions ofthe preservative or other chemical compositions in a fashion whichoffered a number of benefits namely;

-   -   The preservative or other chemical composition uptake is        significantly lower than that normally associated with        vacuum/pressure impregnation of lumber    -   The preservative or other chemical composition can be applied by        simple inexpensive plant and equipment without recourse to        vacuum and pressure processes    -   The preservative or other chemical composition may be created as        required thus minimising the total volume required and thus        minimising potential impact on workers or the environment.

Example 3

This example relates to a process wherein the substrate is constrainedin a chamber above atmospheric pressure and the substrate heated usingradio frequency energy.

Example 3A

Green lumber is placed in an autoclave and the doors closed. An overpressure within the autoclave of 30 pounds per square inch is applied.The increased pressure is applied using any gas and is most economicallyair. Energy is then applied in the form of radio frequency energy,preferably at a frequency below 100 MHz, and more preferably at apressure of between 27 to 40 MHz. This allows immediate heating of thesubstrate, without need for venting or a slow heat up. In addition, nocondensate is created in this process because no live steam is appliedand because any water within the substrate is constrained due topressure conditions. After a time when sufficient energy has beenapplied to achieve the desired temperature throughout the substrate (orexample 130 degrees Celsius), the pressure is rapidly released whereuponwater within the substrate will boil causing evaporative loss and alsogenerating internal pressure which causes mass flow of free woodmoisture and clears the substrate of certain cellular structures anddebris. After allowing controlled moisture loss, preferably with minimaltemperature loss, the vessel is flooded with preservative fluid at atemperature lower than that of the substrate. Fluid is drawn into thesubstrate. The vessel is then drained of surplus fluid and the treatedsubstrate removed. Additional use of pressure or vacuum sequences may beused but are not essential to the process.

Example 3B

Green lumber is placed in an autoclave which is then hermeticallysealed. Energy is applied in the form of radio frequency energy,preferably at a frequency below 100 MHz and more preferably at awavelength of between 27 to 40 MHz. This creates an increase in pressurewithin the autoclave due to steam generated by heating of the substrateand thermal expansion of air in the autoclave. Some condensate iscreated during pressure development but is minimal compared toconventional steaming or kiln conditioning. Continuation of the processis then similar to and subject to the same variations as Example 3A.

Subsequent to removal from the vessel (after the processes of Example 3Aand 3B above) the treated substrate may still retain some energy. Thismay benefit the drying of the substrate and the fixation of thepreservative within the substrate.

Example 4

In many countries it is a requirement to treat less durable wood specieswith preservatives to prevent attack by insects or wood degrading fungi.Also it is frequently required that lumber used for framing, joinery andother purposes by kiln dried to eliminate distortion. These tworequirements are normally incompatible because dried lumber when treatedwith the likes of water based preservatives will again become wet, thusnecessitating re-drying which is costly. Further it is impractical touse some common preservatives such as boron salts because these migrateout of the wood again during re-drying.

The final moisture content required of purveyors of treated lumber isaround 15%-20% based on the dry weight of the lumber. This amounts toaround 70 kilograms of water per cubic metre for lumber with a basicdensity of 440 kilograms per cubic metre. Frequently the lumber is driedsubstantially below this moisture content and is either reconditioned oris allowed to re-equilibrate to the desired moisture content.

Alternatively, a process known as LOSP is prescribed wherein thepreservative material is dissolved in a Light Organic Solvent which isimpregnated into the already dry lumber. This process is very expensiveand liberates copious volatile organic compounds from the lumber intothe atmosphere subsequent to treatment. These solvents are flammable andthis creates another hazard.

One aspect of the present invention relates to the treatment of alreadydry lumber with moisture content of approximately 15% or below. Duringprocessing the moisture content of such wood is further reduced. Upontreatment of the lumber according to the present invention the moisturecontent will increase but will not exceed the range required by the 0purveyor.

For example, in New Zealand it is a requirement that lumber used forframing of buildings be treated to a specific standard. That standardallows use of boron salts with a required retention of 0.4% as boricacid based on the dry weight of lumber. Treatment by traditional vacuumpressure impregnation techniques necessitates application of more than100 litres of aqueous solution per cubic metre. Even if the lumber wereabsolutely dry prior to treatment the final moisture content wouldexceed the standard required because 100 litres of moisture contributes23 percent moisture content.

Using the process of our invention one can achieve low liquid retentionsand yet apply adequate preservative, as is demonstrated by this example.

Kiln dried Pinus radiata lumber samples of dimensions 100 mm×50 mm by150 mm length were prepared in a laboratory. The initial moisturecontent was 7%. The ends were sealed with two applications of a surfacecoating to prevent end effects during the impregnation process.

The samples were heated in a conventional microwave oven for varioustimes at various power levels, held for controlled periods to allowtemperature equilibration, and then submerged for various times in anaqueous preservative containing boron salts.

A large range of data were generated with a selection listed in Table 2below.

TABLE 2 Heating time Stand time Dip time Uptake Sample Power (watts)(seconds) (seconds) (seconds) (L/m³) 1 400 30 15 120 10.53 2 400 60 15120 21.42 3 400 90 30 120 26.78 4 200 70 15 120 12.19 5 200 150 15 12025.04 6 200 140 20 180 22.66 7 200 120 15 180 17.69

In the above cases the fluid was an aqueous solution containing boricacid at 10% by weight. All of the samples with an uptake greater than17.6 litres per cubic metre exceed the required boric acid retention.

The above data is a limited set of the work carried out. We have foundthat uptake achieved by the process is a function of the energy input,the delay between heating and exposure to the preservative fluid, andthe extent of exposure to that fluid.

For example, multiple linear regression analysis applied to a large setof data indicated the following relationship:

Uptake,L/m³=4.24×Energy−0.0145×Stand Time+0.0555×Dip Time−5.21

where Energy was in kWh, and Stand Time and Dip Time were in seconds.

For this data set the value of R² was 0.687 and standard error was 5.66L/m³. This analysis showed that stages of the process could becustomized to target a desired absorption.

Example 5

A group of mini packets of high temperature kiln dried Pinus radiatawere assembled each from 12 individual boards of material of width 100mm and thickness 50 mm. These mini packets of lumber were exposed to RFenergy of 1000 watts for 30 minutes sufficient to apply 100 kilowattseconds of energy per kilogram of substrate. Each mini packet was thenimmediately immersed in a fluid containing 15 percent boric acidsolution. The measured uptake of fluid was 30 litres per cubic metre.Two hours subsequently the moisture had in part evaporated giving afinal equivalent moisture uptake of 20 litres per cubic metre.

Each sample piece was cut in cross section 1 week later and spot testedwith curcumin. The spot tests indicated that the boron fluid hadpenetrated into the core of practically all samples. Similar lumbersamples dipped in the same solution without prior RF energy treatmenthad a very narrow annulus of penetration of approximately 1 mm aroundall surfaces.

Re-treatment of kiln dried lumber with waterborne solutions has alwaysbeen very difficult because known processes always resulted in highuptakes. This then resulted in substantial change to overall moisturecontent and to dimensional stability. The inventor has surprisinglyfound that final moisture content resulting from the process of thisinvention resulted in a minor change of around 4 percent on wood weight.More surprisingly the dimensional change was less than 0.5 percentchange in width and less than 1 percent change in thickness. This iswithin normal production tolerance.

In this embodiment of the invention the inventor has achieved a very lowuptake using waterborne solutions yet have treated the lumber samplesadequately.

It should be noted that with a method of the invention (whether inrelation to green or dry substrate) the final uptake of composition mostpreferably includes a fluid volume which replaces any moisture losswhich may occur during the period of energy application and stand timebefore fluid application, in addition to the net fluid gain which isapparent between start and finish of the method. While this component ismore significant when the process is applied to green or wet substrateit may also be an important aspect for dry substrate, in that theprocess may be manipulated to increase total fluid uptake withoutsignificantly increasing net change in moisture content. This isparticularly important where dimensional change associated by swellingfrom carrier absorption is to be minimized. Of course, it will beappreciated that there may be instances where maintenance ormanipulation of moisture content of the substrate is not critical orimportant.

The inventor has concluded that a process or method described herein canoffer a practical and inexpensive alternative to impregnate poroussubstrates, more particularly lumber, and which can significantly reducethe cost of capital plant otherwise associated with such methods.

Surprisingly, by using a process of the present invention, the inventorfound a ‘significant enhancement in biocide penetration intolignocellulosic substrates without recourse to vacuum or pressuremethods. The enhanced penetration observed by the inventor is believedto have both commercial and environmental consequences. If thepreservative or chemical composition is able to impregnate the substratewithout recourse to vacuum and pressure pumps plant and the cost thereofis significantly reduced. This might be achieved by using lower volumesof preservative or chemical compositions and this has an environmentalbenefit because of reduced risk of spill or loss into the environment.

A further advantage of the present method where the treating solution ismaintained at a low volume and is prepared as required is that therewill be little recycle. Accordingly, there will be minimal problems, ifnot none of the problems, that may be encountered with recycle in largetreatment plants.

The invention has been described herein, with reference to certainpreferred embodiments, in order to enable the reader to practice theinvention without undue experimentation. However, a person having anordinary or general skill in the art will readily recognise that many ofthe components and parameters may be varied or modified to a certainextent without departing from the scope of the invention. Furthermore,titles, headings, or the like are provided to enhance the reader'scomprehension of this document, and should not be read as limiting thescope of the present invention.

The entire disclosures of all applications, patents and publications,cited above and below, if any, are hereby incorporated by reference.

The reference to any prior art in this specification is not, and shouldnot be taken as, an acknowledgment or any form of suggestion that thatprior art forms part of the common general knowledge in the field ofendeavour to which the invention relates in New Zealand or any othercountry.

Throughout this specification, unless the context requires otherwise,the words “comprise”, “comprising” and the like, are to be construed inan inclusive sense as opposed to an exclusive sense, that is to say, inthe sense of “including, but not limited to”.

1. A method of delivering an aqueous composition to a kiln driedlignocellulosic substrate, the method comprising at least the steps of:a. heating a target zone of the substrate using radio frequency energyor microwave energy, and b. applying the composition to a surface of thesubstrate comprising or immediately adjacent to the heated target zone;wherein the composition is at a temperature below that of the heatedtarget zone at the time the composition is applied, the differencebetween the temperatures of the composition and the heated target zonebeing sufficient to reduce pressure in the substrate after thecomposition is applied, allowing for an uptake of less than 100 I/m³ ofthe composition into the substrate.
 2. A method as claimed in claim 1,wherein the kiln dried substrate has an initial moisture content of lessthan 15%.
 3. A method as claimed in claim 1, wherein the substrate islumber.
 4. A method as claimed in claim 1, wherein the frequency of theradio frequency energy is substantially 100 MHz or below.
 5. A method asclaimed in claim 4 wherein the frequency of the radio frequency energyis from substantially 27 MHz to substantially 40 MHz.
 6. A method asclaimed in claim 1, wherein the target zone of the substrate is heatedto a temperature such that there is a temperature differential of atleast approximately 80 degrees Celsius between the target zone and thecomposition at the time of application.
 7. A method as claimed in claim6, wherein the temperature differential is at least approximately 100degrees Celsius.
 8. A method as claimed in claim 1, wherein thecomposition is applied at ambient temperature.
 9. A method as claimed inclaim 1, wherein the target zone comprises a volume of the substrateincluding an area of the surface of the substrate to a depth of betweensubstantially 0.1 cm and substantially 4 cm.
 10. A method as claimed inclaim 1, wherein the target zone of the substrate is heated and held atan elevated temperature for a period of time prior to application of thecomposition.
 11. A method as claimed in claim 10, wherein the substrateis held at an elevated temperature for a period of time sufficient toheat substantially the whole target zone to a substantially uniformtemperature.
 12. A method as claimed in claim 10, wherein the period isa time sufficient to sterilize at least the target zone of thesubstrate.
 13. A method as claimed in claim 1, wherein the methodfurther comprises the step of controlling loss of moisture from thetarget zone of the substrate during step a. or during any period priorto step b. within which the target zone of the substrate is held at anelevated temperature.
 14. A method as claimed in claim 1, wherein thecomposition is a biocidal composition, is a composition that impartsproperties of higher density or strength to at least a target zone ofthe substrate, or a waterproofing composition.
 15. A method as claimedin claim 14, wherein the composition is of a polymeric or pre-polymericnature.
 16. A method as claimed in claim 1, wherein the composition isapplied to the substrate by one or more of dipping, deluging, spraying,or brushing.
 17. A method of delivering an aqueous composition to alignocellulosic substrate the method comprising at least the steps of:a. heating a target zone of the substrate using radio frequency energyor microwave energy, and b. applying the composition to a surface of thesubstrate comprising or immediately adjacent to the heated target zone;wherein the lignocellulosic substrate has a moisture content of lessthan 15% as a weight proportion of dry weight prior to the heating stepand the composition is at a temperature below that of the heated targetzone at the time the composition is applied, the difference between thetemperatures of the composition and the heated target zone beingsufficient to reduce pressure in the substrate after the composition isapplied, allowing for an uptake of less than 100 I/m³ of the compositioninto the substrate.
 18. A method as claimed in claim 17, wherein thesubstrate is lumber.
 19. A method as claimed in claim 17, wherein thefrequency of the radio frequency energy is substantially 100 MHz orbelow.
 20. A method as claimed in claim 19, wherein the frequency of theradio frequency energy is from substantially 27 MHz to substantially 40MHz.
 21. A method as claimed in claim 17, wherein the target zone of thesubstrate is heated to a temperature such that there is a temperaturedifferential of at least approximately 80 degrees Celsius between thetarget zone and the composition at the time of application.
 22. A methodas claimed in claim 21, wherein the temperature differential is at leastapproximately 100 degrees Celsius.
 23. A method as claimed in claim 17,wherein the composition is applied at ambient temperature.
 24. A methodas claimed in claim 17, wherein the target zone comprises a volume ofthe substrate including an area of the surface of the substrate to adepth of between substantially 0.1 cm and substantially 4 cm.
 25. Amethod as claimed in claim 17, wherein the target zone of the substrateis heated and held at an elevated temperature for a period of time priorto application of the composition.
 26. A method as claimed in claim 25,wherein the substrate is held at an elevated temperature for a period oftime sufficient to heat substantially the whole target zone to asubstantially uniform temperature.
 27. A method as claimed in claim 25,wherein the period is a time sufficient to sterilize at least the targetzone of the substrate.
 28. A method as claimed in claim 17, wherein themethod further comprises the step of controlling loss of moisture fromthe target zone of the substrate during step a. or during any periodprior to step b. within which the target zone of the substrate is heldat an elevated temperature.
 29. A method as claimed in claim 17, whereinthe composition is a biocidal composition, a composition that impartsproperties of higher density or strength to at least a target zone ofthe substrate, or a waterproofing composition.
 30. A method as claimedin claim 29, wherein the composition is of a polymeric or pre-polymericnature.
 31. A method as claimed in claim 17, wherein the composition isapplied to the substrate by one or more of dipping, deluging, spraying,or brushing.